1. Field of the Invention
This invention relates to special cationic layer compounds of the hydrotalcite type, to a process for their production and to their use as co-stabilizers for halogen-containing plastics stabilized in particular with calcium and/or zinc salts.
It is known that halogen-containing plastics or molding compounds produced from them tend to degrade or decompose on exposure to heat or ultraviolet light. To counteract this, heavy metal compounds based on lead, tin, barium and/or cadmium are normally used. For reasons of factory hygiene, however, there is a need to replace these thoroughly effective stabilizers by less health-damaging materials. Possible alternative stabilizers to the heavy metal compounds are, for example calcium and zinc soaps, but unfortunately they do not perform as well as the heavy metal compounds mentioned above so that co-stabilizers have to be used in order to enhance their stabilizing effect.
2. Discussion of Related Art
German patent DE-C-30 19 632 describes the use of hydrotalcites for inhibiting the thermal or ultraviolet degradation of halogen-containing thermoplastic resins. This patent specification discloses test results which show that, when readily commercially available hydrotalcites are incorporated, for example, in vinyl chloride resins, they accelerate the dechlorination of the resins on heating or even cause decomposition, blackening or foaming of the resins. In addition, it was found that these hydrotalcites show poor dispersibility in the resins and adversely affect the rheological properties of the resins during molding and also the appearance of the molded products obtained. These test results are attributed to the small crystal size of the usual hydrotalcites and to the large specific BET surface of at least about 50 m.sup.2 /g and the coverage of the hydrotalcite particles with water. Accordingly, it is proposed in German patent DE-C-30 19 632 to use hydrotalcites which have a large crystal size and a specific BET surface of no larger than 30 m.sup.2 /g and which may optionally be coated with an anionic surfactant, such as sodium stearate. European patent application EP-A-189 899 also describes resin compositions containing hydrotalcites having specific BET surfaces below 30 m.sup.2 /g. It is known from this European patent application that the hydrotalcites can be modified with higher fatty acid esters, anionic surfactants and coupling agents of the silane or titanium type in order to improve the compatibility of the hydrotalcite with the resins. According to cited European patent application EP-A-189 899, the hydrotalcites are said to be modified by mechanical mixing with the modifying agents in pure or dissolved form.
DE-C-33 06 822 teaches that hydrotalcites with the formula [Mg.sub.6 Al.sub.2 (OH).sub.12 ](CO.sub.3).sub.3.4H.sub.2 O are obtained by reaction of "active" aluminium hydroxide with magnesium hydroxide or magnesium oxide in the presence of basic magnesium carbonate as carbonate ion donor at a temperature of 50 to 100.degree. C. and subsequent spray drying from the suspension. This process presupposes the availability of "active" aluminium hydroxide which can be obtained, for example, by precipitation from aluminium salt solutions and storage in gel form. Accordingly, this process involves an additional production step (precipitation and washing out of the aluminium hydroxide gel) or makes it necessary to obtain such a gel from a manufacturer and hence to transport large quantities of water which adversely affects the economy of the process.
U.S. Pat. No. 4,656,156 describes a process for producing hydrotalcite in which the aluminate liquor of the Bayer process is used as the aluminium component. The Bayer liquor is reacted with "active" magnesium oxide which can be obtained, for example, by calcining magnesium carbonate. This process can only be economically used in places where the Bayer liquor itself accumulates because otherwise relatively large quantities of water would again have to be transported.
DE-A-15 92 126 describes the production of hydrotalcites from different starting materials, for example from a suspension of solid aluminium hydroxide, solid magnesium hydroxide and sodium hydrogen carbonate. The reactions are carried out in batches and the products are separated from the water phase by filtration or centrifugation and washed before they are dried. The filtration or centrifugation of the very fine-particle reaction products and their subsequent washing are both complicated and time-consuming process steps which add significantly to the production costs.
The problem addressed by the present invention was to provide co-stabilizers for halogen-containing plastics which
would be compatible with calcium and/or zinc compounds, PA1 would be dispersible in halogen-containing plastics without adversely affecting their rheological properties, PA1 would be capable of effectively trapping the decomposition products of halogen-containing plastics and PA1 would be inexpensive to produce, PA1 A) polyols containing 3 to 30 carbon atoms and at least two hydroxyl groups, PA1 B) esters of partly or completely epoxidized unsaturated carboxylic acids containing 6 to 22 carbon atoms, PA1 C) full and partial esters of polyols containing 3 to 30 carbon atoms and 2 to 12 hydroxyl groups with carboxylic acids containing 6 to 22 carbon atoms, PA1 D) alkyl and aryl phosphites, PA1 E) anions of saturated or unsaturated fatty acids containing 6 to 22 carbon atoms, PA1 F) polymers with a molecular weight of 500 to 50,000 which are soluble in water with pH values above 8.
and a process for the production of these co-stabilizers.